JP2002537621A - Storage of erasable / rewritable optical data in photorefractive polymers - Google Patents

Abstract

(57) Abstract: A laser beam from a laser (10) operated in either pulsed or continuous wave mode is focused on a photorefractive polymer material (32) by optics (11-18) to form a material 2. Recording data by causing photon excitation, which can subsequently be erased by irradiating the material with radiation having a wavelength in the ultraviolet or visible spectrum, thereby erasing the recorded data; A method for storing / rewritable optical data is provided. Also disclosed are novel photorefractive polymer materials having relatively narrow absorption bands used in the method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to optical data storage, and more particularly to erasable photorefractive polymers.
The present invention relates to storage of rewritable three-dimensional optical data.

[0002] Multilayer (three-dimensional) optical memories have become an increasingly remarkable area in the development of high-density optical data storage devices. Systems utilizing multi-layer recording can achieve recording densities 100 to 10,000 times higher than conventional optical data storage devices.

[0003] The use of 2-photon excitation in three-dimensional (3D) bit optical data storage has grown due to its ability to increase density in a given material by reducing the dose of recorded bits. The establishment of a two-photon excitation is proportional to the square intensity of the incident light; this effect produces an excitation only in a small area of focus. As a result, there is little crosstalk between adjacent data layers. Another advantage of 2-photon excitation is the reduction of multiple scattering through the use of radiation at infrared wavelengths so that more layers can be recorded along the depth of the capacitive material.

[0004] Over the years, different materials have been used for 3D bit data storage under 2-photon excitation. 2-photon 3D recorded on photopolymerizable and photobleachable materials
Bits have shown that the recording density can reach terabits per cubic centimeter; unfortunately, both materials are not erasable. Cornell Research
ch Foundation, Inc. US Patent No. 5,289, assigned to
No. 407 describes a 3D optical data storage method that uses a beam of coherent light to cause 2-photon photopolymerization of an analyte gel, resulting in a bead of polymerized material in the gel having a different refractive index than the surrounding gel material. Disclose. However, this change is irreversible, so the data bits are not erasable.

[0005] Both photochromic materials that undergo changes in the isomer state and photochromic polymers that undergo a change in refractive index upon 2-photon excitation are erasable materials. Another type of material that is of considerable interest is photorefractive materials. The photorefractive effect results in a modulation of the index of refraction at the focal point, which upon illumination is induced by the spatial distribution of the charges.

[0006] Such a change in the refractive index in the photorefractive material can be reversed by irradiating the medium again with radiation, causing a uniform redistribution of the charge and erasing the recorded information. It is known. However, this is the conventional, photorefractive crystal expensive to manufacture, for example, lithium Nyobu acid (LiNbO ₃₎
Only achieved in

[0007] It is therefore desirable to provide a method for writing and erasing optical data on relatively inexpensive materials.

In one aspect of the invention, a beam of focusable coherent light is produced; focusing the beam on a photorefractive polymer material to provide a 2-photon excitation of the material at the focus of the beam. Causing the data to be recorded by modulating the index of refraction at the focal point, and then irradiating the material with radiation to erase the recorded data; and a method of writing and erasing optical data. Is provided.

According to another aspect of the present invention, a beam of coherent light is focused on a photorefractive polymer material to cause a two-photon excitation of the material at the focus of the beam, thereby producing a refractive index at the focus Modulating the data to write data; irradiating the material with radiation to erase the recorded data; focusing another beam of coherent light on the photorefractive material, and focusing the material at the focus of the beam. Causing a two-photon excitation, thereby modulating the index of refraction at the focal point to rewrite the data to the photorefractive material; and providing a method of writing and rewriting optical data to the photorefractive polymer material. Is done.

In the method of the present invention, 2-photon excitation causes a change in the spatial distribution of charge at the focal point, thereby modulating the refractive index of the material at the focal point.

Preferably, the photorefractive polymer material used in the method is such that irradiation with electromagnetic radiation in the ultraviolet (UV) or visible light spectrum results in a uniform redistribution of the spatial distribution of charges forming the data bits. It is like erasing recorded data when it occurs. The photorefractive polymer is preferably arranged to absorb radiation only in a narrow band in the ultraviolet or visible region of the electromagnetic spectrum. The creation of a narrow absorption band will reduce the material's susceptibility to degradation from the readout process or from incident ultraviolet radiation (eg, from sunlight).

The laser can be used in a pulsed mode, or a continuous wave laser can be used to write data by 2-photon excitation of a photorefractive material. Ultrashort pulse laser beams are typically used for 2-photon excitation. Because the cooperative nature of 2-photon excitation requires the use of high peak power lasers to produce effective excitation. However, the use of ultrashort pulse lasers increases the cost of the recording device and makes it difficult to produce a compact system. The present inventors have shown that 2-photon excitation under continuous wave (CW) irradiation is possible. Although the average power required for CW excitation is increased by almost two orders of magnitude compared to ultrashort pulse irradiation, the use of continuous wave irradiation is fast, low cost and compact, erasable 2-photon 3D bit optical data Allows a storage system to be achieved.

The photorefractive material preferably comprises a chromogen that provides absorption in the ultraviolet or visible range. The polymer can also be doped with a photosensitive material that provides absorption in the ultraviolet or visible region of the electromagnetic spectrum. In one embodiment, the polymer can include poly (N-vinylcarbazole) (PVK). In another preferred embodiment, the polymer can include poly (methyl methacrylate) (PMMA). Each of these polymers has 2,4,7-trinitro-9-
A photosensitive material such as fluorenone (TNF) can be doped. One preferred chromogen is 2,5-dimethyl-4- (p-nitrophenylazo) anisole (DMNPAA), which also provides absorption and electro-optical effects in the ultraviolet to visible region. The polymeric material can also include a plasticizer, such as N-ethylcarbazole (ECZ), to reduce the glass transition temperature of the material.

In the present invention, the recorded bits of data are confocal microscopy utilizing a source of coherent light at the edge or outside wavelength of the absorption band of the photorefractive polymer material,
It can be read out by using a differential interference contrast (DIC) microscope and / or a phase microscope.

According to a further aspect of the present invention there is provided a photorefractive polymer material for use in an erasable optical data storage method, said photorefractive polymer material providing absorption in the ultraviolet or visible region of the electromagnetic spectrum, wherein: , The absorption band of the photorefractive material is 2
It is possible to record data by photon excitation, read bits of data by the edge of the absorption band or an external source of coherent light, and erase bits of data by irradiation with radiation within the absorption band. The polymer material is
Preferably, it comprises a polymer such as PVK or PMMA. The material can include a chromogen that provides absorption in the ultraviolet or visible region of the electromagnetic spectrum.
If desired, the polymer can be doped with a photosensitive material that provides absorption in the ultraviolet or visible region of the electromagnetic spectrum, and a plasticizer can be added to lower the glass transition temperature of the material.

Preferably, the new photorefractive polymer material according to the second aspect of the present invention comprises an amount of the following materials in an amount substantially falling within the following range of percent of the total weight of the photorefractive polymer material: Including at least some: 25% -100% polymer such as PVK or PMMA; 0% -60% chromogen such as DMNPAA; 0% -5% photosensitive material such as TNF; and 0% -40. % Plasticizer such as ECZ.

Re-writable / under 2-photon excitation resulting in a 3D optical data storage system
Preferred embodiments of the present invention using inexpensive photorefractive polymers as recording materials for erasable 3D bit optical data storage will now be described by way of example with reference to the accompanying drawings.

One example of a new photorefractive polymer material that has been used to demonstrate rewritable / erasable 3D bit optical data storage is a photorefractive material 2 that provides absorption in the ultraviolet or visible region of the spectrum. , 4,7-Trinitro-9-fluorenone (TNF
) -Doped polymer poly (N-vinylcarbazole) (PVK).
The photorefractive material, as a chromogen, is 2,5-dimethyl-4- (p-nitrophenylazo) anisole (DMNPAA) which also provides absorption in the ultraviolet or visible range.
) Is also included. In this experiment compared to the previous experiment, the randomly oriented chromogen was not aligned by applying an electric field (poling) during polymerization and manipulation. The poling of the material requires the creation of a magnetic field across the surface of the polymer. Such a uniform magnetic field is difficult to maintain across the surface of large polymer samples and increases the complexity of manufacturing new photorefractive polymers. Finally, N-ethylcarbazole (ECZ) was added to lower the glass transition temperature of the material. One preferred concentration of the material DMNPAA: PVK: ECZ: TNF is 50: 33: 16: 1 by weight of the total weight of the photorefractive material, but different proportions of the constituent materials are within the ranges specified above. It will be appreciated that it can be used. A 100 μm thick uniform film was produced by combining all the materials by Teflon cast and then polymerizing PVK at 90 ° C. for 2 days. The obtained polymer block was cut and polished to obtain a sample used in the experiment.

Another example of a new photorefractive polymer material that has been used in rewritable / erasable 3D bit optical data storage is a photosensitive material 2,4 that provides absorption in the ultraviolet or visible region of the spectrum. Polymer poly (methyl methacrylate) (PMMA) doped with 7-trinitro-9-fluorenone (TNF). Photorefractive materials, as chromogens, also provide absorption in the ultraviolet or visible range.
Also includes dimethyl-4- (p-nitrophenylazo) anisole (DMNPAA). In this experiment, randomly oriented chromogens were not aligned by applying an electric field (poling) during polymerization and manipulation. No such polling electric field is required. This is because the local electric field at the focus created by the high numerical aperture objective lens is five orders of magnitude greater than that of the incident light across the objective lens aperture. This local electric field is strong enough to induce a detectable electro-mechanical effect.

Finally, N-ethylcarbazole (ECZ) was added to lower the glass transition temperature of the material. One preferred concentration of the materials used, DMNPAA: PMMA: ECZ: TNF, was 10: 73: 16: 1 by weight of the total weight of the photorefractive material, but different proportions of the constituent materials were within the specified range. It will be appreciated that it can be used. Combine all materials in a Teflon cast, then
By polymerizing the PMMA at a temperature of 65 ° C. for 2 days, a thickness of 10
A 0 μm uniform film was produced. The obtained polymer block was cut and polished to obtain a sample used in the experiment.

FIG. 1 shows the absorption bands of a 100 μm thick sample of a new photorefractive polymer material based on PVK detected on an Oriel UV-Vis spectrophotometer using a Xenon arc lamp light source. The absorption bands of photorefractive polymer materials based on PMMA are almost identical.

FIG. 1 shows that the absorption band maximum of the new material is within 380-600 nm. Therefore, a laser beam with an infrared wavelength of 800 nm can be used in the recording process to generate 2-photon excitation at 400 nm. Recording wavelengths can fall substantially within the range of about 750 nm to about 1200 nm. The absorption band substantially cuts off the wavelength of 630 nm, so that the absorption band is about 630 nm to about 1 nm.
A wavelength range of 200 nm can be selected to read recorded photorefractive data bits without subjecting to single- or 2-photon excitation. A wavelength of about 750 nm can be used. However, the power of the read beam is single or 2-
It should be low enough not to cause photon excitation.

Referring to FIG. 2, an optical system for two-photon recording of a beam of data in a photorefractive polymer material is shown. The recording system consists of a laser (10), a mechanical shutter (11) linked to a computer (20), a lens (12,1).
3), a pinhole aperture (14), another aperture (16), and an objective lens (
18). For confocal geometry readout, the system uses a beam splitter (
22), an additional lens (24), another pinhole aperture (26) and a detector (28) also linked to the computer (20). A three-dimensional scanning stage (30) is provided for placing a sample of photorefractive material (32). The scanning stage (30) can move in x, y and z directions under the control of the computer (20).

In the recording process, Spectra-Physics Tsunami
A Ti: sapphire laser (10) was focused on the photorefractive polymer sample (32). The laser was used in pulsed mode to record the bit patterns of FIGS. 3 and 4 on PVK photorefractive polymer material. In a mode-locking operation, the laser can produce an ultrashort pulse beam with a pulse width of 80 fs and an average power of 800 mW. The laser was operated in continuous wave (CW) mode to record the patterns of FIGS. 5 and 6 in PMMA photorefractive polymer material. In each case, the wavelength of the laser was tuned to 800 nm, which corresponds to twice the wavelength of the main absorption band of the sample. From the absorption curve in FIG. 1, we see that at a wavelength of 800 nm,
It can be seen that there is no photon absorption and only 2-photon absorption can occur at a wavelength of 400 nm. The logical state of the recorded information is determined by the computer (20)
Controlled by a mechanical shutter (11) linked to Recording material (32)
Is the Melles Griot computer-controlled 3D interpretation stage (30)
It was installed in. For recording, Zeiss Fluar objectives (FIGS. 3 and 4) with numerical apertures of 0.75 and 0.70 and magnification of 20, respectively, and an Olymp
The us UPlan APO objective (FIGS. 5 and 6) (18) was used.

To read the change in refractive index caused by the 2-photon photorefractive effect,
Using an Olympus Fluo View microscope, differential interference contrast (
(DIC) mode. To read the recorded information, 632.8 nm H
An e-Ne laser was coupled to the Fluo View. Because 6
The wavelength of 32.8 nm is at the edge of the absorption band and does not cause minimal damage to the recorded information (see FIG. 1). To erase the area, the area of interest was irradiated with UV light from a mercury lamp in a Fluo View microscope. A numerical aperture of 0.7 and a magnification of 20 were provided for both reading and erasing (FIGS. 3 and 4).
Or Olympus with a numerical aperture of 0.4 and a magnification of 10 (FIGS. 5 and 6).
An UPlan APO objective (18) was used.

As evidence of the ability to record information as a change in refractive index using 2-photon excitation, FIGS. 3 (a) and 3 (b) show the measured change in refractive index produced at the focal point. In recording, information was recorded using an average power of 5 mW at the focus. 2
A pattern (character C) consisting of 4 × 24 bits was recorded on the sample. Bit separation is 3
. 2 μm, and the exposure time for each bit was 25 ms. In the recording process, a laser beam power of less than 5 mW is scanned across the sample to obtain a DI
A C image was generated. FIG. 3B shows the deterioration of recorded information after scanning 500 times. The contrast of the recording bit in FIG. 3B is 90% of that in FIG. This feature indicates that the information is slightly erased due to the absorption of the light used for recording. The information recorded in FIG. 3 (c) corresponds to FIG. 3 (a) and FIG.
The same powers and exposure times as used in b) were used. FIG. 3D shows 1-2.
3C shows the same area observed in FIG. 3 (c) after exposure to ultraviolet radiation for a second.
The result indicates a complete erasure of the previously recorded information.

FIG. 4 illustrates the ability of the system to record and read changes in the refractive index of multiple layers of information. 3
Layer information was recorded by laser separation at 10 μm. Each layer has a pattern of 24 × 24 bits. The first layer recorded near the surface consists of the pattern of the letter "A". The second and third layers each consist of the letters "B" and "C", thus:
The retrieved 3D data density is approximately 10 gigabits / cm ³ , which is comparable to that previously achieved with photochromic polymers, photorefractive crystals and photobleaching materials.

FIG. 5 (a) shows the ability to record information as a change in refractive index using continuous wave 2-photom excitation. In recording, information was recorded using an average power of 75 mW at the focus. A pattern (character E) consisting of 24 × 24 bits was recorded on the sample. The bit separation was 5.6 μm, and the exposure time for each bit was 2 ms. A laser beam of less than 5 mW was scanned across the sample in the reading process to produce a DIC image. FIG. 5 (b) shows the same area observed in FIG. 5 (a) after exposure to UV radiation for 1-2 seconds. The result indicates a complete erasure of the previously recorded information. In FIG. 5C, a character (F) of a new pattern is written in the same area as used in FIGS. 5A and 5B. 2
Five artifacts are marked with circles 1 and 2 in FIGS. 5 (a), (b) and (c), indicating that the information was erased and rewritten using the same area.

FIG. 6 shows the ability of this system to record and read changes in the refractive index of multiple layers of information. Three layers of information were recorded with a 25 μm layer separation. Each layer has a pattern of 24 × 24 bits. The first layer recorded near the surface contains the pattern of the letter "A". The second and third layers consist of the letters "B" and "C", respectively.

From the first half, the present invention provides a method of recording and rewriting data using pulsed or continuous wave (CW) 2-photon excitation and erasing recorded data by irradiating with ultraviolet or visible radiation of electromagnetic radiation. It has been found that it provides an effective method of recording, reading, erasing, and rewriting three-dimensional data in relatively inexpensive photorefractive polymer materials.

It will also be appreciated that various modifications, changes and improvements may be made to the preferred embodiment described above without departing from the scope and spirit of the invention.
Such modifications or improvements that would increase the storage capacity of the system include: 1. Compensation for small amounts of crosstalk between layers (see FIG. 4) due to spherical aberration from refractive index mismatch between recording material (n = 1.75) and immersion medium (n = 1). As a result of the refractive index mismatch, the size of the commentary spot in a deep part of the capacity recording medium increases. As a result, depending on the depth of the recording medium, a series of axial peaks will occur, thus causing crosstalk between adjacent data layers. This problem could be overcome, thereby increasing the data density by using a variable tube length method.

[0032] 2. Instead of a Ti: sapphire laser operating at CW concentration, other types of continuous wave (CW) laser beams can be used to produce 2-photon excitation. For example, with the help of a 1.2W CW laser diode operated at near infrared wavelengths, a fast, low cost, compact, erasable 2-photon 3D bit optical data storage system can be achieved.

[0033] 3. Different photorefractive polymers can be used, and the chemical properties of the material can be modified, leading to increased stability of the photorefractive polymer. By adjusting the absorption spectrum, we can determine the wavelength of light that affects the material. Creating a narrow absorption band in the ultraviolet or visible region will reduce the material's susceptibility to degradation from the readout process or from irradiation from incident ultraviolet light (ie, sunlight).

[0034] 4. A method for increasing the density of a 2-photon data storage system by using a recording method can be based on the polarization state of a recording beam. This technology is
Upon reading, using a different polarization state of the recording beam, where only bits having the appropriate polarization state are detected, it is possible to record multiple bits at the same location in the material.

5.2—Selective bit erasure methods in photon data storage systems can be based on the polarization of the recording and reading beams. Individual bits can be selected and erased by changing the polarization state of the recorded bits so that it has the appropriate polarization state that can be detected or not detected on readout.

[Brief description of the drawings]

FIG. 1 is a graph showing an absorption curve of a photorefractive polymer material used in the present invention.

FIG. 2 is a schematic diagram of a 2-photon excitation microscope used to record data bits on a photorefractive polymer.

FIG. 3 (a) shows a 24 × 24 bit pattern of the letter “C” recorded on the photorefractive polymer PVK by 2-photon excitation in the first reading, and FIG.
The same area after reading out 0 times, (c) is a 24 × 24 pattern of the character “A”, and (d) is the same area as (c) after being exposed to ultraviolet irradiation, and the stored information is completely FIG. 3 is a photographic view showing the erasures.

FIG. 4 shows a 24 × 24 bit pattern recorded at different depths in a photorefractive polymer PVK using 2-photon excitation, (a) showing a first layer containing the letter “A”. ,
(B) shows the second layer containing the letter “B”, (c) shows the third layer containing the letter “C”,
FIG.

FIG. 5 (a) shows a bit pattern of “E” recorded on another photorefractive polymer (PMMA) by 2-photon excitation, (b) (a) after exposure to ultraviolet radiation
3C is a photographic view showing the erasure of recorded information in the same area as in FIG. 1), and FIG. 3C is a photographic view showing the bit pattern of the character “F” written in the same area as in FIGS.

FIG. 6 shows bit patterns recorded at different depths on a photorefractive polymer PMMA using 2-photon excitation, where (a) shows a first layer containing the letter “A” and (b) )
FIG. 4 is a photographic diagram showing a second layer containing the character “B”, and FIG. 4C is a photographic diagram showing a third layer containing the character “C”.

[Procedure for Amendment] Submission of translation of Article 19 Amendment of the Patent Cooperation Treaty

[Submission date] June 23, 2000 (2000.6.23)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Contents of correction]

[Claims]

45. The photorefractive polymer material of claim 44, wherein said PMMA; DMNPAA; TNF and ECZ are present in a concentration of 73: 10: 1: 16, which is about less than or equal to the total weight of the photorefractive polymer material. .

[Procedural Amendment] Submission of translation of Article 34 Amendment

[Submission date] November 24, 2000 (2000.11.24)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Contents of correction]

Preferably, the new photorefractive polymer material according to the second aspect of the present invention comprises an amount of the following materials in an amount substantially falling within the following range of percent of the total weight of the photorefractive polymer material: A polymer such as 25% -99.5% PVK or PMMA, including at least some; a chromogen such as 0.5% -60% DMNPAA; a photosensitive material such as 0.5% -5% TNF. And a plasticizer such as 0-40% ECZ.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Contents of correction]

[Claims]

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID , IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW (72 ) Inventor Day, Daniel John Australia, 3051 Victoria North Melbourne, Cousin Street 7/100 (72) Inventor Smallridge, Andrew John Australia, 3187 Victoria East Brighton Melosa Avenue 3F Term (Reference) 2H048 DA04 DA23

Claims (44)

[Claims] Providing a focusable beam of coherent light; focusing the beam on a photorefractive polymer material to excite the material at the focal point of the beam, thereby refracting at the focal point. Recording the data by modulating the rate; and then irradiating the material with radiation to erase the recorded data; and a method of writing and erasing optical data. 2. Focusing a beam of coherent light on a photorefractive polymer material and 2-photon exciting the material at the focus of the beam, thereby:
Writing data by modulating the refractive index at the focal point; irradiating the material with radiation to erase recorded data; focusing another beam of coherent light onto the photorefractive polymer material and Writing and re-writing optical data to the photorefractive polymer material characterized by 2-photon excitation of the material at the focus, thereby modulating the refractive index at the focus and rewriting the photorefractive material; How to write. 3. Data recorded by irradiating the photorefractive material with an electromagnetic wave having a wavelength of ultraviolet (UV) light or the visible spectrum to cause a redistribution of the spatial distribution of the charges forming the bits of the data. 3. The method according to claim 1, wherein 4. The method of claim 3 wherein the photorefractive index polymer material absorbs radiation only in a narrow band in the ultraviolet or visible region of the electromagnetic spectrum. 5. The absorption band of the photorefractive polymer material has a maximum of about 380 nm.
5. A method according to claim 3 or claim 4 wherein the method substantially falls in the range from about 600 nm to about 600 nm. 6. The method according to claim 3, wherein the photorefractive polymer material does not substantially absorb radiation above a wavelength of about 630 nm. 7. The method of claim 1, wherein the data recorded in the photorefractive polymer material is read by irradiating the photorefractive polymer material with coherent light having a wavelength substantially in the range of about 630 nm to about 1200 nm. Item 7. The method according to any one of the above items. 8. The beam of focusable coherent light used to record data on the photorefractive material has a wavelength substantially in the range of about 750 nm to about 1200 nm, and comprises a 2-photon beam. A method according to any one of the preceding claims, which causes the excitation. 9. The method according to claim 1, wherein the data is recorded on the photorefractive polymer material using a pulsed laser beam. 10. The method according to claim 1, wherein data is recorded on the photorefractive polymer material using a continuous wave laser beam. 11. The method according to claim 1, wherein the polarization bits of the data are recorded on the photorefractive polymer material using a focusable coherent light polarized light beam. 12. A plurality of bits are recorded at the same position having different polarization states in the photorefractive index polymer material using different polarization states of the recording light beam.
The described method. 13. The method according to claim 11, wherein the bits of the recorded data are read using a readout beam having an appropriate polarization state. 14. The method according to claim 11, wherein individual bits of the data are erasable by the polarization state of the individual bits. 15. The method of any preceding claim, wherein the photorefractive polymer material comprises at least about 25% polymer by weight of the total weight of the photorefractive material. 16. The method of claim 1, wherein the photorefractive polymer material comprises a chromogen that provides absorption in the ultraviolet or visible region of the electromagnetic spectrum. 17. The method of claim 1, wherein the photorefractive polymer material comprises a photosensitive material that provides absorption in the ultraviolet or visible region of the electromagnetic spectrum. 18. The method of claim 1, wherein the photorefractive polymer material comprises a plasticizer that lowers the glass transition temperature of the material. 19. The method according to any one of the preceding claims, wherein the photorefractive polymer material comprises at least some of the following in amounts that fall substantially within the following percentages of the total weight of the photorefractive material: 25% -100% polymer; 0% -60% chromogen; 0% -5% photosensitive material; and 0% -40% plasticizer 20. The method according to claim 1, wherein the polymer is poly (N-vinylcarbazole) (PVK).
20. The method of claim 15 or claim 19 comprising: 21. The polymer as claimed in claim 21, wherein the polymer is poly (methyl methacrylate) (PMMA).
20. The method of claim 15 or claim 19 comprising: 22. The method according to claim 16, wherein said chromogen comprises 2,5-dimethyl-4- (p-nitro-phenylazo) anisole (DMNPAA). 23. The method according to claim 17, wherein the photorefractive material comprises 2,4,7-trinitro-9-fluorenone (TNF). 24. The method according to claim 19, wherein said plasticizer comprises N-ethylcarbazole (ECZ). 25. A photorefractive polymer material for use in a method for storing erasable optical data, said photorefractive polymer material providing absorption in the ultraviolet or visible region of the electromagnetic spectrum, wherein the photorefractive The absorption band of the absorptive material can be recorded as a bit of data by two-photon excitation, read a bit of data by a source of coherent light at the edge or outside of the absorption band, and erase a bit of data by irradiation with radiation within the absorption band. The material characterized in that: 26. The photorefractive polymer material of claim 25, wherein the absorption band maximum of the photorefractive material substantially falls in the range of about 380 nm to about 600 nm. 27. The upper end of the absorption band of the photorefractive polymer material is about 630n.
27. The photorefractive polymer material of claim 25 or claim 26. 28. The method according to claim 19, wherein the material is at least about 25% by weight of the total weight of the photorefractive material.
28. The photorefractive polymer material according to any one of claims 25 to 27, comprising: 29. The photorefractive polymer material according to claim 25, wherein said material comprises a chromogen providing absorption in the ultraviolet to visible region of the electromagnetic spectrum. 30. The chromogen comprises from about 0.5% to about 6% by weight of the total weight of the material.
30. The photorefractive polymer material of claim 29, which is present in an amount substantially in the range of 0% by weight. 31. A photorefractive polymer material according to claim 25, wherein said material comprises a photorefractive material that provides absorption in the ultraviolet or visible region of the electromagnetic spectrum. 32. The photorefractive polymer of claim 31, wherein said photosensitive material is present in an amount substantially within the range of about 0.5% to about 5% by weight of the total weight of the photosensitive material. material. 33. The photorefractive polymer material according to claim 25, wherein the material comprises a plasticizer to reduce the glass transition temperature of the material. 34. The photorefractive polymeric material of claim 33, wherein said plasticizer is present in an amount substantially in the range of 0% to about 40% by weight of the total weight of the photorefractive polymeric material. 35. A photorefractive polymer material for use in a method for storing optical data, the material comprising an amount of less than or equal to substantially less than a percentage of the total weight of the photorefractive polymer material. Said material comprising at least some of said material. 25% -99.5% polymer; 0% -60% chromogen; 0% -5% photosensitive material; and 0% -40% plasticizer 36. The polymer as claimed in claim 36, wherein the polymer is poly (N-vinylcarbazole) (PVK).
36. The photorefractive polymer material according to claim 28 or claim 35, comprising: 37. The polymer as claimed in claim 37, wherein the polymer is poly (methylmethacrylate) (PMMA).
36. The photorefractive polymer material according to claim 28 or claim 35, comprising: 38. The chromogen comprises 2,5-dimethyl-4- (p-nitrophenylazo) anisole (DMNPAA).
7. The photorefractive polymer material according to any one of 7. 39. The photorefractive polymer material according to claim 31, 32 or 35 to 38, wherein said photosensitive material comprises 2,4,7-trinitro-9-fluorenone (TNF). 40. The photorefractive polymer material according to claim 33, wherein said plasticizer comprises N-ethylcarbazole (ECZ). 41. The following materials: poly (N-vinylcarbazole) (PVK); 2,5-dimethyl-4- (p-nitrophenylazo) anisole (DMNPA)
A); A photorefractive polymer material for use in a method for storing optical data, comprising: 2,4,7-trinitro-9-fluorenone (TNF); and N-ethylcarbazole (ECZ). 42. The photorefractive material of claim 41, wherein said PVK; DMNPAA; TNF and ECZ are present in a concentration of about 33: 50: 1: 16 by weight percent of the total weight of the photorefractive material. 43. The following materials: poly (methyl methacrylate) (PMMA); 2,5-dimethyl-4- (p-nitrophenylazo) anisole (DMNPA)
A); A photorefractive polymer material for use in a method for storing optical data, comprising: 2,4,7-trinitro-9-fluorenone (TNF); and N-ethylcarbazole (ECZ). 44. The photorefractive polymer material of claim 43, wherein said PMMA; DMNPAA; TNF and ECZ are present in a concentration of 73: 10: 1: 16 by weight, which is less than or equal to the total weight of the photorefractive polymer material. .